A cm is always a cm. A "size 8" is not always a size 8. This guide explains the actual mechanics behind every converter on this site — why some conversions are exact and others are educated guesses, and how to tell which is which before you trust a number.
Every size on this site falls into one of two fundamentally different categories, and knowing which one you're looking at tells you how much to trust a conversion.
Measurement-anchored sizes describe an actual physical quantity: a shoe size is built around foot length in centimeters, a bra band around ribcage circumference in inches or centimeters, a shirt collar around neck circumference, a suit size around chest circumference, a kids' EU clothing size around height. Convert these between countries and you're really just converting units — inches to centimeters, or one numbering convention for the same length to another. That's why a US 34 bra band is always an EU 75, and a men's US 40 suit is always an EU 50: there's a real length underneath both numbers, and it doesn't change.
Label-based sizes describe nothing physical at all — they're a number or letter a brand assigns, and different brands assign it differently. Numeric dress sizes (0–20), letter sizes (XS–XXL), and cup letters above D all fall here. There's no ruler you can hold up to check whether a "10" is really a 10; it's whatever the company that made the garment decided to print on the label.
This distinction is why every result on this site's converters carries either a clean number or a "~ approximate" marker — it's not hedging, it's telling you which kind of size you're actually holding.
Bra band size is measurement-anchored and converts cleanly — but cup size is a hybrid. A, B, C, and D are shared letters across US, UK, and EU sizing, so up to that point cup conversion is as reliable as the band. Past D, the three systems each keep adding letters down their own path, and they stop agreeing:
| US | UK | EU / FR / IT |
|---|---|---|
| A | A | A |
| B | B | B |
| C | C | C |
| D | D | D |
| DD (or E) | DD | E |
| DDD (or F) | E | F |
| G (or DDDD) | F | G |
| H | FF | H |
| I | G | I |
| J | GG | J |
| K | H | K |
Reading a UK "E" as if it were a US "E" is the single most common bra-sizing mistake on the internet — it's actually a US DDD. There's no shortcut here; this table (and the interactive bra converter) exist because the letters genuinely don't translate by pattern-matching.
Because band and cup are two independent measurements, more than one band/cup combination can hold roughly the same cup volume. Go one band size down and one cup letter up, or one band size up and one cup letter down, and you land on a "sister size" — 34B, 32C, and 36A are all sisters of each other. This is genuinely useful when your usual size sells out, or when the cup fits but the band feels a little loose or tight. The bra converter shows both sister sizes automatically once you pick a size.
Numeric dress sizes and letter sizes have a well-documented tendency to drift looser over time and to disagree between brands — often called vanity sizing. A size that fit one way a decade ago, or at one store, doesn't reliably fit the same way somewhere else. There's no fix for this in a lookup table, because the underlying problem isn't a translation error — it's that the label was never tied to a fixed measurement to begin with.
Every page on this site marks a result "~ approximate" whenever it's built from this kind of label-to-label convention rather than an actual unit conversion. When you see that marker, treat the result as a good first guess, and prefer the brand's own measurement chart if it publishes one.
Shoe sizing packs in more ways to go wrong than almost any other garment. US men's and US women's are different scales for the same feet (a US women's 8 and a US men's 6 both fit a 24.5 cm foot) — mixing them up is the single most common shoe-sizing error. UK sizing is a third scale again, and it isn't even the same offset for both genders: UK men's runs one size below US men's, while UK women's runs about two sizes below US women's.
Kids' sizing adds a second twist: US and UK kids' sizes both climb to 13 and then restart at 1 (written 1Y, 2Y… in the US) for bigger kids — a "size 4" could be a small toddler shoe or a much bigger kid's shoe depending on which side of that restart it's on.
Underneath all three scales is one number that never lies: foot length in centimeters. It's literally what the Mondopoint system (used in Japan, and by some military and safety-footwear standards) sizes shoes by directly — no lookup table required, no conversion, just the length itself. That's why this site's shoe converter includes a measure-your-foot tool alongside the usual system-to-system lookup.
Measure the band snugly around your ribcage, directly under your bust, keeping the tape level. Then measure loosely around the fullest part of your bust. One common fitting method: the difference between the two, in inches, gives the cup — a 1" difference is roughly an A cup, 2" a B, 3" a C, 4" a D, and so on up the same divergent alphabet covered above. Brands vary enough that trying a size on beats any formula, but this gets you to the right starting point.
Stand on a piece of paper and mark your heel and longest toe, then measure the distance in centimeters. Most shoes need about 1–1.5 cm of extra room past that number for comfort — the measure-your-foot tool already accounts for this when it recommends a size.
Wrap a soft tape around the base of your neck where a buttoned collar would sit, snug but not tight, then add about half an inch (1.3 cm) for comfortable movement. Round up if you land between two sizes on the collar converter.
Wrap a tape around the fullest part of your chest — under the arms, across the shoulder blades — level and snug but not tight. Match the result on the suit converter; if you're between two sizes, most tailors suggest sizing up since a jacket is easier to take in than let out.
There's no universal formula here, because the size number itself isn't anchored to a measurement — it's a brand's own convention. Measure your bust, waist, and hips, and compare against that specific brand's published size chart when one exists; the numeric conversion on the women's clothing converter is a starting point for which size to try, not a substitute for the brand's own numbers.
Stand your child against a wall, heels to the baseboard, mark the top of their head, and measure floor to mark in centimeters. Match that to the EU column on the kids' clothing converter — it's a more reliable guide than age, since kids of the same age vary in height enormously.
One page per garment, plus a direct pair-page shortcut for the most common single conversions.
A conversion translates one brand's or country's label into another (a US 8 into an EU 40). A body measurement — foot length, bust, chest, collar, height — is the actual physical number a size is supposed to represent. Measurements are always more reliable, because labels are conventions brands can and do disagree on.
Because some conversions really are exact (a shoe's foot length in cm, a bra band in inches-to-cm, a shirt collar in inches-to-cm) while others are brand conventions with no single correct answer (cup letters above D, numeric dress sizes, XS–XXL letters). The approximate marker is this site's way of never hiding that difference.
A sister size is a different bra band/cup combination with roughly the same cup volume — one band size down with one cup letter up, or vice versa. 34B, 32C, and 36A are sister sizes of each other, useful when your usual size runs out or the band feels slightly off.
As a starting point, quite useful; as a guarantee, not very. Measurement-anchored sizes (shoes, bra bands, collars, chest, height) are close to exact. Label-based sizes (numeric dress sizes, letter sizes) vary by brand and have drifted over time — always prefer a brand's own measurement chart when one is available.